In the book, there is a minor side plot where Percy was hiding the fact that he had a Ravenclaw girlfriend named Penelope Clearwater, who was also attacked at the same time Hermione was. She is largely out of the movie, but in one scene, Nearly Headless Nick says hello to Percy and 'Miss Clearwater' walking side by side.

Though very obvious to British users of this site, it is most likely not as well known in the US. Fawkes the phoenix is most likely named for Guy Fawkes (1570-1606), a Catholic conspirator who tried to kill King James I and blow up Parliament in 1605 (the Gunpowder Plot) to avenge persecution of Roman Catholics in England. His plan failed, and he was arrested, tried, and executed. November 5th is Guy Fawkes night/bonfire night, when the failure of his plan is celebrated with fireworks and bonfires - the fires often have a "guy" on top of them, a stuffed dummy.

The reason Susan Bones is in so many scenes with the Gryffindors, although she was sorted into Hufflepuff, is because the actress is Eleanor Columbus, the daughter of director Chris Columbus. Two of his other children are also in the movie.

The line "I didn't know you could read" was improvised by Tom Felton.

When Harry uses the Floo powder and ends up in Knockturn Ally, the first thing he looks at is a necklace. If you read the 6th book( you will know that Katie Bell (a Gryffindor) touches a necklace from Knockturn Ally. The same one from this movie.

There's been some discussion whether Lucius Malfoy starts saying "Avada-" or "Vera-" after Harry freed Dobby. It's not so easy to decide in the English version, although the DVD subtitles say "Vera-". In the German version, it's a lot easier, he says "Avada-" without any doubt. So it seems either the translators did not read the original script, or Malfoy does say "Avada-" in the English version (and they tried to cover it up for some reason by using a different subtitle). For those who have not read past book three, "Avada" is the first part of the spell "Avada Kedavra", a powerful killing spell that is highly illegal in the wizarding world. This is why this piece of trivia is important - many fans are perplexed as to why dear Lucius was performing such a spell directly outside Dumbledore's office.

All of the scenes that included Richard Harris were done first because of his failing health (he eventually died from Hodgkin's disease on October 25, 2002 after filming was completed). The scene where Dumbledore and Harry are in his office at the end of the movie was done first because he had the most dialogue here (notice how young Harry looks in this scene).

As Harry looks at the album at the start of the film, he turns the page of wax paper, between the pages of photos and the imprint on the wax paper is clearly visible. The imprint is that of many spider webs on the thin page of wax paper. It is best seen frame by frame.